This book explores the possible economic implications of large shifts in the supply of foreign-born, hired farm labour that could result from substantial changes in U.S. immigration laws or policies. Hired labour is an important input to U.S. agricultural production, accounting for about 17 percent of variable production expenses and about 40 percent of such expenses for fruit, vegetables, and nursery products. Over the past 15 years, roughly half of the hired labourers employed in U.S. crop agriculture have lacked the immigration status needed to work legally in the United States. Thus, changes in immigration laws or policies could lead to markedly different economic outcomes in the agricultural sector and the market for hired farm labour. The same is generally true for other economic sectors that rely on large numbers of unauthorised workers.